Optical system for spotlights



Aug. '11, 1942.

c. w. cLARKsON OPTICAL SYSTEM FOR SPOTLIGHTS Filed Sept. 25, 1941Patented Aug. 11, 1942 UNITED STATS PTEEN T OFFICE 2,293,014 OPTICALsYsTEM FOR SPOTLIGHTS Clarence W. Clarkson, Washington, D. C.

Application September 25, 1941, Serial No. 412,226

2 Claims.

(Granted under the act of `March 3, 1883, as amended April 30, 1928; 370O1. G. 757) The invention described herein, `if patented maybemanufactured and used by or for the Government for governmental purposeswithout the payment of any royalty thereon.

The present invention relates to light projectors and particularly to anovel and improved optical system for spotlights.

In prior art devices of this character known to the inventonit has beenacustom to provide a light source and a condensing lens to intercept aportion of the light rays emitted from the source and focus them into aparallel beam.

In some instances, an intensifying mirror has been used, usually in theform of a spherical segment positioned immediately behind the lightsource with its center of curvature coincident with the center of thelight source. The major portion of the light. emitted from the source,however, isv ordinarily not intercepted by either the lens or mirror andis absorbed as heat by the projector walls. It is obvious that theabsorption of a large percentage of the rays` emitted from the lightsource is highly disadvantageous in that it not only decreases theefllciency of the prolector but also in that the generation of a largeamount of heat from the absorption of the rays is objectionable. 1

It` is, therefore, the primary object of this invention to provide anovel and improved optical system for spotlights whereby all of the raysemitted from a light source may be accurately focused in the same manneras rays directly impinging the lens, in order to utilize substantiallyall of the light rays emitted from the light source.

Another object of this invention is to provide a novel and improvedoptical system for spotlights whereby all of the rays emitted from alight source and` not directly impinging the lens are redirected throughone or morereflecting surfaces and thence through the exact center ofthe light source to permit them to be accurately focused.

A further object of the invention is to provide a light sourcepositioned at' one of the foci of an elliptical'reilector having anaperture concentric with the axis of the ellipse whereby a portion ofthe rays from the light source are directly emitted through the apertureas a primary beam, and all rays net within the primary beam impinge thereflecting surface and are redirected through the light source again, tobe then emitted as a partl of the primary beam to intensify the beam.

The single figure of the drawing is a sectional View of a spotlight.

Referring now to the drawing accompanying and forming a part of thisspecification, the light source I0, illustrated as an incandescent lamp,

is positioned so that the center of its filament lies at one of the fociF1 of an elliptical reflector Il. The interior surface of the reflectorIl consists of a highly polished reflecting surface formed in a trueelliptical shape about the foci F1 and F2. An aperture |21 is providedat the forward end of the reflectorV andis concentric with the axis ofthe foci F1 and F2, it being under-- stood, of course, that thereflector l`l is circular in transverse cross-section so that allpointsof the reflector are concentric with a line through the foci F1 and F2so that these points constitute primary and secondary focal points ofthe reilector. A Ventilating aperture I3 is provided at the opposite endof the reflector Il, and a spherical reflector I4 is Vmounted onbrackets I5 to intercept all rays of light falling in the rearmost areaof the reflector. The reflector I4 is positioned with its center ofcurvature coincidentwith the focal point F1 for reasons to behereinafter pointed out.

The entire assembly of the light source llland reflector Il are mountedon a base I6 by means of a socket l'l and bracket IB and the base I6 isarranged for longitudinal sliding movement Within the housing 2l byhandknob 22 threaded on a, clamping screw 23 adapted to slide in afocusing slot 2d at the bottom of the housing. rThe casting 25 closesthe rear of the housing, while a casting 2B which closes the front ofthe housing is provided with a flange 2lin which a condensing lens 28 ismounted.

The operation of the optical systemof the device is as follows:

When the filament of the light source lll is energized, light rays willbe emitted in all directions frorn the point F1 so that all rays fallingin certain portions of the solid angle surrounding the light source willbe intercepted by the reflector l l, but all rays included within theangle A will be emitted through the aperture l2. The major portion ofthese will directly impinge the condensing lens 28 to be focused into abeam, which we may designate as a simple or primary beam. The path of atypical ray of light of this beam is indicated in the drawing by thereference numerals R1, which shows the ray directly emitted from thepoint F1 passing outwardly through the condensing lens. The condensinglens l0 concentrates the numerous rays to form a substantiallycone-shaped beam, but it will be understood, of course, that as thefocusing knob 22 is moved rearwardly, the rays designated by the numeralR1 will approach parallelism until, when the center of the light sourceIB reaches the center of focus of the lens 2B, all of the rays R1 willbe concentrated into a spotlight beam of substantially parallel rays.

All of the rays from the source F1 which are emitted within thespherical angle B indicatedv in the drawing will impinge the interiorsurface of the elliptical reflector ll and will be reflected twice,finally being redirected again through the point F1 and outwardlythrough the aperture I2 to intensify the primary beam heretoforedescribed. The path of a typical ray falling within this angle isillustrated in the drawing by the lines R2, which show the ray firstdirected upwardly to impinge the reflector I l at the point 3 I, thencedirected downwardly through the focus F2 to impinge the reflector againat the point 32 and thence be reflected again through the focal point F1and outwardly through the condensing lens 23. Inasmuch as the ray passesdirectly through the focal point F1 immediately before impinging thelens, it possesses the same optical characteristics and may be focusedin a manner identical with rays originally emitted from the lightsource. The rays emitted within the solid angle B will thus serve tointensify the primary beam and may be focused as a part of the primarybeam.

All rays of light emitted from the source I3 within the spherical angledesignated as C in therdrawing will be reflected on the interiorsurfaces of the elliptical reflector II four times before being emittedfrom the aperture I2, but when so reflected will be directed through thefocal point F1, immediately before impinging the condensing lens 28 andwill thus also intensify and form a part of the beams heretoforedescribed. A typical path of one of the rays falling within the angle Cis designated by the line R3 wherein the ray impinges the reflector I Iat the point 33, passes through the focus F2 to the point 34, thencethrough the focus F1 to the point 35, thence through the focus F2 to thepoint 33, and finally through the light source II] on the focal point F1and outwardly through the condensing lens 28.

All rays of light emitted from the source I within the angle D willimpinge the spherical reflector I4, and since this reflector has itscenter of curvature coincident with the focal point F1, these rays willbe reflected squarely backwardly through the focal point F1 and thencethrough the condensing lens 28 to further intensify the beam. The pathof a typical ray falling within this angle is illustrated in the drawingby the line R4, wherein it will be seen that the ray emitted from thesource I will first impinge the spherical reflector I4 at the point 31and will be directed backwardly through the source I0 and through thecondensing lens 2B. It will be noted that the spherical reflector I4bears a denite dimensional relationship with the aperture I2 of theelliptical reector, since the angle about the second focus F2 subtendedby the reflector I4 is equal to and opposite of the angle intercepted bythe aperture I2 with respect to the focal point F2. A From the foregoingdescription, it will be obvious that practically all of the light raysemitted from the light source I0 may be utilized in the formation of asingle beam of parallel rays, it being understood, of course, thatalthough the device is illustrated in the drawings in its position whenused as a floodlight to project a divergent cone-shaped beam, yet whenthe center of focus of the light source I0 and the focal point F1 aremoved to the center of focus of the condensing lens 28, all of the rayspassing through the focus F1 and impinging the condensing lens 28 willbe focused into a cylindrical beam of parallel rays. Thus, by followingthe teachings of this invention, it is entirely practicable to utilizein a focusing spotlight projector a far larger percentage of the totallight emitted from the source than has heretofore been regarded aspracticable. Further, this may be accomplished without dilliculties dueto unwarranted dispersion of the rays, since each ray will be projecteddirectly through the original center of the light source and thus eachray, no matter how often reflected, will have the same characteristicswhen it finally leaves the source of light as the rays originallyemitted therefrom.

. Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. In a light projector, in combination, an elliptical rellector havingsmooth polished interior light-reflecting surfaces and including alightprojecting aperture at the front end of said reflector and aVentilating aperture at the rear end of said reflector, both of saidapertures being concentric with the axis of projection of the beam, thearrangement being such that the two foci of the elliptical reflector liein substantial spaced relationship with each other on the said axis ofprojection, the projection aperture being positioned forwardly of bothof said foci; a spherical reflecting surface at the rear end of theelliptical reflector and opposite from the projection aperture, saidspherical reflector being of smaller diameter than the projectionaperture and arranged to subtend a solid angle with respect to the rearfocus of the elliptical reflector opposite and equal to the anglesubtended by the projection aperture with respect to the rear focus; alight source located at the front focus of the elliptical reflector, acondensing lens positioned exterially of and in front of the projectionaperture and spaced apart from said aperture, the lens being coaxialwith the light source, the elliptical reflector and the sphericalreflector; common mounting means to maintain the light source, sphericalreflector and elliptical reflector in fixed relation positions withrespect to each other, and adapted to simultaneously shift the lightsource, the spherical reflector and the elliptical reflector withrespect to the condensing lens, to alter the optical characteristics ofthe projected light beam.

2. In a light projector, in combination, an elliptical reilector havingsmooth polished interior light-reflecting surfaces and including alightprojecting aperture at the front end of said reflector, saidaperture being concentric with the axis of projection of the beam, thearrangement being such that the two foci of the elliptical reflector liein substantial spaced relationship with each other on the said axis ofprojection; a spherical reflecting surface at the rear end of theelliptical reflector and opposite from the projection aperture, saidspherical reflector having its center of curvature coincident with thefront focus cf the elliptical reflector and being of smaller diameterthan the projection aperture; a light source located at the front focusof the elliptical reflector; a condensing lens; and common mountingmeans to maintain the light source, spherical reflector and ellipticalreflector in fixed relative positions with respect to each other, andadapted to simultaneously shift the light source, the sphericalreflector and the elliptical reflector with respect to the condensinglens, to alter the optical characteristics of the projected light beam.

CLARENCE W. CLARKSON.

